What Causes Abnormal Menstrual Bleeding Post Birth Control Patch Implantation?

Idea got the birth control in my arm and it is sapose to last for 3 years. I got it four months ago. Just recently I started spotting and for the last two weeks I have had my period non-stop but it comes out do dark it s almost black and it has a really bad smell to it and sometimes its red. And after I have sex with my boyfriend it seems to get worse what is wrong with me????